In general, a construction machine such as an excavator is constructed such that a hydraulic pump is driven by means of an engine to drive an actuator with the hydraulic pressure, but with this construction, fuel efficiency thereof is poor and environmental problems such as noise, exhaust gas and the like occur, because works are executed while the engine output is largely varied correspondingly to large variation in load under work.
Therefore, in recent years, hybrid construction machines and control apparatuses thereof (Japanese Unexamined Utility Model Publication No. Hei 5-48501, Japanese Unexamined Patent Publication No. Hei 10-42587, etc.) have been developed and suggested, in which the engine is connected to an electric motor or a power generator to convert a part or whole of the engine output into electric power, power remaining in working with a light load is charged into a battery and the power is withdrawn from the battery to use in working with a heavy load. With this construction, for example, as shown in FIG. 12, because varying part of work load (work energy) could be smoothed by means of charge and discharge of the battery, variation of the engine output could be suppressed as small as possible even when the work load (work energy) is largely varied, to thereby realize improvement of the fuel efficiency and reduction of noise and exhaust gas
However, in the above conventional construction, because the electric motor could not be driven when power could not be obtained from the power generator or the battery due to breakdown of the engine, the power generator, the battery and the like, operations after that time could not be executed. Therefore, for example, if the excavator is out of order when a boom is in a raised state, the boom stops in the raised position, the excavator must be left in this state until repair of the excavator is completed, and thus, safety could be threatened.
Also, the construction machine, specifically, the excavator is required to perform various works different in work load, such as excavating, making even, sloping a bank, scattering and the like. Therefore, unless a relationship among the kinds of works described above, the engine output and the charged state of the battery is considered, there occur problems such as waste of energy, deterioration of the battery, reduction of work efficiency and the like.
Therefore, a first object of the present invention is to provide a hybrid construction machine capable of assuring safety thereof by emergency driving electric motors when power cannot be obtained from a power generator or a battery due to breakdowns thereof.
A second object of the present invention is to provide a control apparatus of a hybrid construction machine capable of preventing deterioration of batteries due to excessive charge or discharge when executing various works different in load.
A third object of the present invention is to provide a control apparatus of a hybrid construction machine capable of suppressing reduction of work efficiency while preventing deterioration of batteries due to excessive discharge as small as possible.